1. Field of the Invention
This invention relates to the removal of sulfur dioxide and sulfur trioxide from gaseous streams. In another aspect, this invention relates to the treatment of aqueous glyoxylic acid solutions. More particularly, this invention relates to processes for the removal of sulfuric acid or absorbed sulfur trioxide from aqueous glyoxylic acid solutions, and to processes for the removal of sulfur dioxide and sulfur trioxide from industrial flue gases using aqueous glyoxylic acid solution as an absorbent.
2. Summary of the Prior Art
The use of sulfur-containing fossil fuels as power sources results in effluent gases containing a number of noxious environmental pollutants, among which are sulfur dioxide and to a lesser extent sulfur trioxide. Similarly, tail gases from sulfuric acid production processes also contain objectionable amounts of sulfur dioxide and sulfur trioxide. A host of solutions to this problem has been proposed. The non-regenerative methods involve absorbing and/or reacting the sulfur oxides with inorganic reagents, e.g. alkaline carbonates or hydroxides, in slurry or solution to yield the corresponding sulfite and sulfate salts. Such non-regenerative gas treating systems, however, are characterized by high costs due to the continuing chemical consumption and the high transportation costs required for continually bringing the chemicals to the plant site and the disposal costs for continually removing the sludge formed. See, for example, U.S. Pat. No. 3,632,306.
Other general methods suggested for the selective removal of sulfur dioxide and sulfur trioxide from effluent gases utilize absorbents which can be regenerated, such regeneration offering significant advantages economically over non-regenerative processes.
Such regenerative absorbent systems include inorganic systems such as sodium solution processes and magnesium slurry processes. Regenerative organic bases, e.g. amines, have also been suggested as absorbents. See, for example, U.S. Pat. Nos. 3,047,364 and 3,904,735. A different class of absorbent has also been proposed, namely aqueous solutions of glyoxylic acid. See, for example, U.S. Pat. No. 3,350,165. It will be noted that this U.S. Pat. No. 3,350,165 states that aqueous solutions of glyoxylic acid perform, in addition to a good absorbent role for sulfur dioxide, the role of an oxidation inhibitor with respect to the sulfur dioxide, such that the formation of sulfuric acid is inhibited. Even so, it has been found that, because most industrial flue gases containing sulfur dioxide also contain sulfur trioxide, that sulfur trioxide is also absorbed by the aqueous glyoxylic acid solution, thus in fact creating sulfuric acid in the system. The sulfuric acid remains in the aqueous glyoxylic acid solution after stripping of the sulfur dioxide from the aqueous glyoxylic acid solution. Unless removed, the concentration of sulfuric acid in the absorbent will increase to an intolerable level, causing corrosion of the equipment and degradation of absorbent.